Does that mean, before spending, I dont have to transfer manually some amount from old addresses
to the newest address in order to have one address which holds at least the same amount
as the price of the acticle i intend to buy?
You might want to read what i have wrote earlier:
You can combine as much inputs to as much outputs as you wish (limited by size, logic, etc..).
[...]
Logically, you therefore don't have to consolidate them first.
Your wallet simply picks some UTXO's for you (e.g. from 'old' AND 'new' addresses) and creates a transaction.
Also.. there is no 'newest' or 'oldest' address. All addresses are equal.
You don't have to move your coins between your addresses at all. Just simply receive coins, and later send coins.
Your wallet will handle everything for you.
And is this consolidation of UTXOs totally free (no transaction fees)?
Of course it is not free. This is a normal on-chain transaction.